Light stencil and method of making same



Aug. 28, 1 945. B, R'U N CK 2,383,568

LIGHT STENCIL AND METHOD OF MAKING SAME Filed May 10, 1943 BINDINGMATERIAL (zmcmnmum oxIoE aIIsEI //A 11 WIQN QfiQWC II$SYQ MASKINGMATERIAL (ALUMINUM BASE) I I I I I x z I I TRANSPARENTBACKING SHEETBINDING MATERIAL (ZN 0, TI Q2 BASE) MASKING MATERIAL (ALUMINUM sAsEITRANSPARENT BACKING SHEET LIGHT SENSITIVE FILM PRIMER GOAT (ZN O,TI 02BABE) MASKING MATERIALIALUNINIIN BASE) TRANSPARENT BACKING SHEETORIGINAL I ASTER CONTACT EXPOSURE OF NEGATIVE ORIGINAL MASTER NEGATIVESENSITIZED AND SENSITIZED BLANK BLANK D EVELOPED COPY I alterations inthe delineated marked or printed in black Patented Andes, 194s -8nomsmcn. sun mrrnon or MAKING sans Benjamin Rudnick, Huntington, toRepublic Aviation Corporation,

tion of Delaware Y.,alllgnor aoorpora- Application my 10, 19 4s, SerialNo. man

11 claims, (01. 41-46) This invention relates carried on a transparentwhich may hence be designated as to stencils of the proved light-stencilof this type which can be backing sheet or plate,

light-stenoils," and particularly aims to provide an imused repeatedlyas a negative for'the photo-mechanical reproduction of line-drawings,mechanical layouts,-templates, etc. In general the present inventioncontemplates a light stencil or photo-mechanical negative hav-. in! npaque reproduced may be delineated in transparent or clear lines,capable of repeated reproduction in positive prints or as the basis forthecreation of duplicate negatives or secondary negatives embodying anydesired changes,

design. More specifically, an object of the invention is to provide anopaque light-stencil orphoto-mechanical negative on the surface of whichany, kind 'of line drawings may first be roug ly sketched and outlinedby means of a stylus, so as to form a transparent master negative, whichmay be repeatedly used for the preparation of accurate positive copies,

or reproductions of said negative or for the reproduction thereofonmetal sheets from which templates can be made. The use of thisphotomechanical stencil or negative'is not, however,

limited to this reproduction of master line-draw ings but, as willbecome will find great utility in machine and sheet metal apparenthereinafter,

1 shop practice in transferring said mechanical master layouts directlyonto the work to be machined, metalsmithed or otherwise operated upon.

Another object is to provide, for alight-stencil, a surface which willform a. suitable contrasting field in which the design to be",

modifications or andmay then be scribed backgrclmd for a pencil sketchor for an outline lines on said surface so as to serve as a guide forthe stylus when scribing the master drawing through said surface.

Another object is to provide. a negative, opaque-surface which will formasuitable primer or sub-stratum for a. photographic emulsion.

A further object is .to provide a light-stencil coating oflight-sensitive which canbe readily duplicated" in whole or in partwith'a high degree of reat saving of time. Y

Among its other objects the instant invention proposes the employment ofa master negative as the basis from which derives .the. method for theproduction of one or more secondary negatives by photographic contactprinting, each of which is a complete replica of the masternegaaocllracy and at a tive except as to such version of the positiveprint of the master negative into a definitive secondary negative all inaccordance with the present invention.

Still another object is to provide a practical method of tracingdirectly from original drawings, .on said light-stencil, an outline ofcertainparts or the entirety of the master line-drawing tobescribed.

Other objects and advantages will become apparent from the followingdetailed description of the preferred embodiment of my invention,reference being had to the accompanying drawing, in which Figure 1 is across-sectional view of a lightstencil usable as a photo-mechanicalmaster negative and prepared according to the preferred mode;

Figure 2 is a similar cross-sectional view showing a light-stencilprepared according to a modiflcation of said preferred mode;

Figures 3 to 6 inclusive show dlflerent steps of the preferred mode ofduplication of the light-' stencils according to present invention,Figure 3 being a. side view, showing-the blank upon which the negativeof Figure 1 is to be duplicated, Figure 4, a cross-sectional section,showing the preferred manner in which the negative of Figure 1 and. theblank of Figure 3 are arranged during their exposure, Figure 5, a sideview of the developed positive, and Figure 6, a cross-sectional sectionof the duplicate light-stencil or master 5 negative thus obtained. 1

1 In Figure 1 of the drawing is illustrated a lightstencil usable asphoto-mechanical master negative or pattern sheet, and comprising: abacking sheet III, made of any suitable transparent ma.- terial': anintermediate coating I l of a suitable pulverulent masking material anda. top coating I! of a suitable binder for said masking material.

Preferably, this light-stencil is prepared with a. clear, transparentplastic sheet .01 to 0.15 thick having a. low linear coefficient ofthermal expansion (0.000059), 1. e. a high dimensional stability. Otherdesirable qualities of this base sheet are:waterproofness,non-flammability, and resistance to inorganic acids andalkalies, to alcohols, oils plastic sheet material obtained bycalendering the resins resulting from the co-polymerization of vinylchloride (CHrtCI-ICI) and vinyl acetate (CHiCOaCECHs) in the presence ofa suitable Plastic pulverulent white pigments, which (by weight) inmixin thin layer I! of said catalyst. A plastic sheet of the foregoingis a standard article of commerce and is'obtainable on the open marketunder the trade-name Vinylite."

As this material is a thermoplastic, it becomes possible to groove orscribe thereon an outline of the design to be reproduced, using awood-burning stylus or other heated tool for this purpose. On the cleantop surface of this base-sheet I is laid a very thin layer of metallic.dark-colored masking material II. This layer is preferably prepared bymixing thoroughly a certain amount of pure, metallic, elementaryaluminum powder, ground sumclently fine to pass a 400-mesh screen, intoa lacquer, such as a mixture of 60% of cellulose acetate and 40% ofmethyl or methacrylate resin, so as to form a thick paste. This latteris then'thinned to the desired consistency by means of a suitablemixture of solvents, such as a. mixture of 60% toluol, 30% ethyleneglycol and of xylol, and is appliedpreferably by means of a spray-guntosaid clean surface of the plastic sheet II. This first coating, ll,dries in a few minutes and, when dry,

sheet l0 completely opaque, but adheres thereto so lightly that it canbe readily removed with a few strokes of a still eraser. One importantresult of the use of such a metallic coating is that it enhances theheatresisting quality of the base sheet and increases its rigidity.

Best results are obtained by mixing the following proportions (byweight) of said insredlents:

Per cent Aluminum powder 6.5

Lacquer 12.25 Solvents 81.25

In any event the nature of the masking coating II, when dry, must besuch that thesheet i0 is rendered completely opaque and the coating llso lightly adhered to the sheet In and the particles of aluminum solightly cohered that the coating may be easily removed by erasing orbrushing. It is to be noted that the use of aluminum powder as themasking agent in the coating ll results not only an exeremely thinmasking coating.

The material for the top coating I2 is prepared by mixing thoroughly, acertain amount of consists with a much greater amount of the samelacquer that was used for the first coating H. To this mixture, is thenadded a smaller amount of the same mixture of solvents that was used insaid first coating II, in order to thin to the desired consistency.

The most satisfactory results have been obtained by using as pigment forthis light-colored top layer II, a mixture of 75% of zinc oxide (ZnO)and 25% of titanium dioxide (T102) and by adhering to substantially thefollowing proportions the different ingredients mainly of zinc oxide,

entering into said top layer l2: 7

1 Per cent White pigmen 16 Lacquer 30 Solvents 54 The liquid varnishthus obtained is substantially more adherent than the metallic lacquerused as masking material for the first coating 1 I. A very varnish isthen appliedby means of a spray-grm-over the preferably II and isallowed to dry, which it does first layer brush or of asoft' in completeopacity but in I renders the tive thus prepared may a,sss,ccs

substantially more slowly than said am coating of masking material.

When dry, this top coating I! has, in a high degree, the followingessential characteristics:

1. It is scribable, i. e., of such a consistency that a sharp, hardpointed instrument, such as a stylus, will readily penetrate into it anwill out then through perfectly clean, sharp and smooth furrowed lines,while it will also take" a sharp, softer-pointed instrument, such as ain pencil without being indented.

2. It forms a convenient white or sharply contrasting background for apencil sketch or for a surface print or photographic reproduction inblack lines to be used as a guide when scribin the permanent drawingwith a stylus.

3. It forms a convenient primer or sub-stratum for a layer oflight-sensitive photographic emulsion, which is spread over it-as willbe described in more detail later on--when it is desired to make apreliminary photographic reproduction of the line-drawing to be scribedtherethrough, or when it is desired to duplicate a master negativedirectly by contact printing.

4. It is of such a consistency that it acts as a binder for the more orless pulverulent masking material of the layer I I. Y

5. It is of such a flexible and homogeneous nature that, when spreadover a furrowed, transparentbacking sheet-as will be described later inreference to Figure 2-it delineates the corrugations, "ups and "downs,"of said furrows, without filling them.

6. It is strongly adhesive and resistant and therefore will not beaccidentally scratched or rubbed off by the draftman's tools, orfingers, or cuffs.

when completely dry, and at on- -even after a long period of storage-thenegabe used in a lofting department or in a shop to record aline-drawing or layout that it is desired tckeep permanently as a masterdrawing or pattern.

The drawing is made on this white surface, II, by first sketching, inpencil, a part or the whole thereof on the surface without penetratingor scratching into it at all, and then cuting through, or detachinglocally, the top layer Ii by means of steel-pointed drawing instruments,such as a stylus, scribers, calipers, compasses, etc., so as to formfurrowed lines I! directly below said pencil lines. With a brush, orpreferably, a soft eraser, the draftsman then brushes or rubs outsimultaneously all the pencil lead, all the binding coating thusdetached, and all the aluminum powder H lying directly underneath thelines I! over the transparent plastice backing ll.

The photo-mechanical master negative thus prepare may then beindefinitely preserved and any number of positive copies may be madetherefrom as occasion demands. Due to the relatively low coefflcient ofthermal expansion of the base sheet ",said copies will always beperfectly accurate.

Figure 2 shows a modification of the preferred mode of preparation of aphoto-mechanical negaany time later due to the transparency of theplastic sheet u, said lines I! are almost invisible, but, when coveredwith a thin layer of masking material and 7 man, when scribing with astylus, the corresponding line-drawing I I through the layer l2.

As a precautionary'measure, it is usually desirable to have a duplicateset of all the master negatives; often series of slightly diiferentderived master negatives have to be prepare by making but a few changesin a basic master negative. Also, it is often desirable to make a'change' or correction in a master negative without destroying the partsthereof which are thus changed or corrected.

Figures 3 to 6 inclusive villustrate how such duplicationpreferablyiscarried out. Figure 3 shows a bare or blank negative I ll, l2, (preparedexactly as the negative III, II, l2 of Figures 1 and 2) adapted forduplicating a part or the whole of an existing master negative merely byaddition of a thin layer l of light-sensitive photographic emulsion onthe top layer II. This sensitized blank is thenplaced in direct contactwith the original master negative to be duplicated, the arrangementbeing preferably that shown in Figure 4, and this latter isphotographically exposed to parallel light rays l1, emanating from a;suitable source ofartificial light (not shown),

arranged above the surface i2.

The parallel rays, i1, pass through the open lines l3, l4 and throughthe transparent backing sheet ill and harden the corresponding portionsl8 of the sensitized layer lot the blank l0, ll,

away, save for the hardened portions l8, which forms then a line drawingcontrasting in black over the white background of the developed positivethus obtained (Figure 5). This drawing re- I2. The photographic llaye'ri6 is then washed 4 produces exactly, the'line drawing l3 of theoriginal master negative.

In order to make a duplicate master negative out of this developed copy,the draftsman, now following the black. linesv l8 as a guide, with hisstylus, readily scribes the drawing through the top layer 12' and thenbrushes away or rubs out with a softeraser, all traces of hardenedemulsion l8, all the detached binding material l3, and all thepulverulent masking material H. The re- 1 sultant duplicate masternegativeis shown in Fi ure 6. a I g Manifestly a secondary negative maybe made as above described and have any desired changes, modificationsor-alterations incorporated therein.

In short the delineated design reproduceafrom] the negative ill-l ll2 onthe secondary negative ill'l l'l2" and represented by the lines ll inFig.15 may be entirely and completely scribed throughthe-binding-coating l2 in agreement g 3 in the cost or the duplicatenegatives, as highly skilled draftsmen are no tracing or scribing thetop layer l2.

oi the line-drawing through Should the draftsman make a mistake inscribfar from being a defect, is, instead, an advantage greatlyappreciated by the supervising and checking organizations which can thusrecognize at a glance that a master drawing has been changed and at oncelocalize and identify the corrections. Manifestly any suitable materialor combination of materials other than those above specified can be usedfor either the masking coating ll-ll' or the binding coating i2-l2' andvar. ious other modifications in the foregoing mode of preparing thelight stencil or photomechanical negative may be made and employedwithout departing from the spirit and scope hereof as defined in theannexed claims.

(In these claims, the expression light-stencil is employed to conciselydefine a stencil comprising a transparent base and an opaque scribablecoating and the expression scribable to concisely define a consistencyand toughness of a coat such that a 4H pencil will not scratch it, whilea stylus will readily cut through said coat, smooth and sharp clearlines).

I claim: 7 1. A blank for the preparation of a light-stencil,comprising: a transparent clear plastic sheet; a first coat of acellulose acetate base lacquer thinned in suitable solvents and mixedwith aluminum dust and spread in -a liquid state over said backingmember; and a second scribablecoating of a light-coloredlacqueroverlying said first coat: the formulation of said first coatbeing such. that, upon evaporation of the solvents. said celluloseacetate base lacquer becomes an integral part of the plastic sheet,while the released aluminum dust forms a readily removable, opaque anddark-colored masking film'evenly overlying aid lacquer-coated backingsheet,

with the lines I8 or part of it may be scribed through the coating I! inagreement with the lines l8 and a modified or altered design created byscribing through the coating I! new continuing and connecting lines.Thus a secondary negative IiY-I-l l'i2' of a new design or layoutincorporating part of the original design or layout is produced which ineffect constitutesa master negative, all without making any change oralteration in the original negative Ill-i I -l 2.

This method of duplication assures a high degree of accuracy witha'minimum of time con sumed. Also, it effectuates considerablesaving 2.A light-stencil for reproducing designs, comprising: a transparentplastic backing sheet, the top surface of which is adapted forreceiving-preliminary designs traced from originals and scribed thereinwith a stylus; a film of masking material so high in surface-tension asto be evenly spreadable over said engraved surface to closely follow theincisions forming said preliminary designs without filling theseincisions; and a scribable coating of a substantially white lacquer sohomogeneous and so .evenly spreadable over said film as to follow thefurrows formed therein over said incisions without filling said furrows;the visible corresponding furrows thus formed in said coating serving asguides for facilitating the permanent scribing of the designs to bereproduced throughout said coating and said film.

3. A light-stencil, comprising: a transparent backing member; a firstcoat prepared of a mix of aluminum in a cellulose acetate base lacquerto form a thick paste, subsequently thinned with a mixture of solventsto a suitable consistency for spreading over said backing member; asecond lacquer coat overlying and binding said film longer required forthe -able binding coating thereon,

Y scribing the delineated design and a design scribed through at leastsaid second coat: said second coat being prepared oi a mix ofsubstantially pure-white pigments in a cellulose acetate base lacquer ina greater amount than was used for the first coat, to thereby iorm athick paste subsequently thinned, with a. smaller amount of the samemixture of solvents than was used for said first coat, to a suitableconsistency for spreadingover said masking film, to thereby form ascriba'ble covering for said film and a white contrasting background fora pencil sketch or outline of said design or for a surface print inblack thereof.

4. The method of making, on a transparent base, a light-stencil forreproducing designs, when traceable originals 01' said designs areavailable, which comprises: securing the transparent base upon saidoriginal design; tracing an outline of said latter in the top surface ofsaid base with a stylus; spreading evenly a liquid film of opaque anddark-colored masking material over said engraved surface; allowing saidfilm to dry to a substantially pulverulent state; binding saidpulverulent film by spreading evenly over it a liquid film of whitelacquer; allowing said lacquer to dry to a scribable consistency;scribing said overlaying a scrib- 6. The method of making aphoto-mechanical negative consisting in covering a transparent sheetwith a-frangible masking coating, overlaying a scribable binding coatingof contrasting color thereon, depositing a light-sensitive photographicemulsion on said binding coating, light printing a design on saidemulsion, developing the latent image thus made, scribing the designthrough the coatings aforesaid in agreement with 2. portion of theimage, and scribing a modification of the original design disregardingthe image so printed but in conjunction with and as continuation of thescribed portion thereof.

7. The method or making a photo-mechanical negative consisting incovering a transparent sheet withan opaque masking coating, depositing ascribable binding coating-thereon, delineating a design by scribing thelines thereof through the aforesaid coatings, contact printing thedesign so scribed on a secondary'negative also comprising a transparentsheet covered with an opaque masking coating, a scribable bindingcoating and a light-sensitive photographic emulsion deposited on saidbinding coatin developing the latent image thus made on the secondarynegative, and scribing the design through the coatirrgs of the secondarynegative in agreement with the lines of the image so printed anddeveloped.

8. The method of making a photo-mechanical negative consisting incovering a. transparent sheet with an opaque masking coating, depositinga s-cribable binding coating thereon, delineating a design by scribingthe lines thereof through the aforesaid coatings, contact printing thedesign so scribed on a secondary negative also comprising a transparentsheet covered with an opaque masking coating, 9. scribalble bindingcoating and a light-sensitive photographic emulsion deposited on saidbinding coating, developing the latent image thus made on the secondarynegative, and scribing through that portion of the image desired to beretained through the coatings of the secondary negative in agreementwith the lines of the image, and scribing additions to the originaldesign through the coatings of the secondary negative in conjunctionwith the first scribed portions of the original design.

9. The method of making a negative for line reproduction consisting inscribing lines to be reproduced through the masking coating of a sheetof negative material to create light passages, printing said lines bythe passage of light through said light passages upon a second sheet ofnegative material having a. light sensitive photographic emulsion and anunderlying scribable' masking coating thereon, developing the latentimage so printed, scribing those portions of 'the image so developed tobe retained in the masking coating of the second negative sheet, andscribing additions or continuations of such portions, as desired, alsothrough the masking coating of the second sheet thereby creating acomplete layout in the form of light passages in the second negativesheet.

10. A method of making a negative for line reproduction consisting ofscribing the lines to be reproduced in a primary negative sheet having ascribable masking coating thereon, contact print- 7 ing said lines on asecondary negative sheet hav- I layering a scribable masking coating andon overlying of photographic emulsion, developing the latent image thusformed, scribing in said masking coating of the secondary negative sheetthose portions of the image to be retained, and such additions,alterations or continuations as are to be incorporated in said secondarynegative.

11. A negative for line reproduction comprising a backing member, acoating containing aluminum dust lightly adhered to said backing memherby lacquer, and an overlying binding coating consisting of lacquer, zincoxide and titanium dioxide.

BENJAMIN RUDNICK.

